Variable resistor



March 1, 1960 M. E. BoURNs VARIABLE RESISTOR Original Filed Jan. l2,1953 INVENToR. MH/P/.H/Y E BOU/EWS United States Patent O VARIABLERESISTOR Marlan E. Bourns, Riverside, Calif;

1o Claims. (Cl. ass-iso) The present invention relates to variableresistors or potentiometer-s, and is a divisio'n of my pendingapplication, Serial No. 330,642, tiled January 12, 1953, now Patent No.2,777,926, entitled Variable Resistor. This invention is primarilyconcerned with high precision instruments of the type used in guidedmissiles, aircraft, and other complex electronic equipment, and theprimary object of the invention is to provide a variable resisto'r orpotentiometer which is extremel-y compact, yet designed for extremelyprecise adjustment, and capable of giving accurately reproducibleresults. i

Another object of the invention is to` provide a variable resistor whichwill withstand acceleration, vibration, and

. extreme ranges of temperature such as an instrument of this type maybe exposed to in aircraft or in guided missile use.

These and other objects and advantages of the invention will becomeapparent to those skilled in the art upon consideration of the following`detailed description or" the preferred forms thereof, reference beinghad to the accompanying drawings, wherein: t

Figure 1 is a longitudinal section through one embodiment of theinvention taken at the planeindicated by the line 1--1 of Figure 2; v

Figure 2 is a transverse sectio'n through the same, taken at 2-2 inFigure 1;

Figure 3 is a perspective elevation of the mandrel member employed inthis embodiment;

Figure 4 is a perspective view of the contact member employed with thisembodiment;

Figure 5 is a plan view of the device vshown in Figure 3, with theresistance and conductor elements in place;

Figure 6 is a longitudinal section through another ernbodiment of theinvention, taken alo'ng the line 6-6 of Figure 7;

`Figure 7 is a transverse section, taken at 7-7 of Figure 6;

Figure 8 is a perspective view of the screw element of this embodiment;and

Figure 9 is a partially sectioned perspective view of the outer caseemployed with this last embodiment.

Attention is directed first to Figures l to 5, inclusive, wherein aninstrument embodying the invention is designated in its entirety by thereference numeral 10, and is seen to co'mprise a tubular case 11, whichmay be of plastic, as shown, having a mandrel 12 rotatably connectedtherewith. The case 11 is internally threaded at 13 to form a helix, andis closed at one end by an end wall 14, having a central socket 15 thatreceives a journal 16 on the end of the mandrel.

The mandrel 12 comprises an end plate 20, having a` portion 21 ofreduced diameter, which projects into the open end of the case 11. Anannular groove 22 is provided in the reduced diameter portion 21, andseating in Y with an annular groove 71, which receives the end Of au,

Patented Mar. 1, 1960 portion 24, of rectangular cross section, projectslengthwise throughthe center of the tubular case 11 fro'm the portion21, and is provided on its inner end with the journal 16 that is seatedin the bearing socket 15 in the end wall 14.

The main body portion 24 of the mandrel has longitudinally extendingchannels 25 and 26 formed inthe top and bottom surfaces thereof, andseated within the top channel 25 is a wire wound resistance element 30.The ends of the wire windings are attached to rivets 31, and joined tothese rivets are terminal wires 32 and 33. It will be noted thatterminal wire 33 returns from the outer end of the element 30 to the endplate 20 alongside the element on a shelf 34.

Slidably mounted upon the mandrel 12 is a slider, or carrier 35 having arectangular opening 36 extending there through to receive the main bodypo'rtion 24 of the mandrel. The outer portion of the carrier 35 isgenerally cylindrical, and is provided with a male thread 40 which isadapted to engage the threads 13 on the inside of the case 11. An endplate 41 is attached to one end of the carrier 35, and projectingaxially therefrom is a spring Contact arm 42, the outer end of whichwipes o'n the top edge of the resistance element 30.

Also projecting upwardly from the bottom portion of the end plate 41into the bottom channel 26 of the mandrel is a tab 43, which isconnected to one end'of `a flexible, extensible coil spring 44, whichserves as an electrical return means from the contact arm 42 to anexternal terminal. The other end of the spring 44 is attached to a thirdterminal Wire 45 extending through a hole in the end plate 2t).v

Thus, when the case 11 is turned with respect to the mandrel, thecarrier 35 is caused to move lengthwise along the resistance element ,30by the threads 13, 40; the said carrier being held against turning bythe sliding engage'rnent of the flat sides of the' opening 36 with thetherein, through which terminal wires 54, 55 and 56l Formed in theinside surface of the cylindrical pass. case is a longitudinallyextending groove 60, which serves to guide the slider, or carrier 61 andprevent the ysame from rotating. l

Projecting from the inner side of the yend wall 52 con centric with theinside surface of the cylindrical case 50 is a semi-cylindricalsupporting member 62 having two parallel, longitudinally extendinggrooves 63 and 64 formed in the at top surface thereof. Seated withingroove 63 is a wire-Wound resistance element 65; while groove 64 has aU-shaped conductor strip 66 seatedl therein, which serves as anelectrical return means. Terminal Wires 54 and 56 are connected to thewindings of the resistance element 65 at opposite ends thereof, whilewire 55 is connected to the conducto'r strip 66.

The tubular screw element 51 is inserted into the open end of thecylindrical case 50, and is sized to tit loosely.

within the space between the inner wall of the case and the cylindricalouter surface of the supporting member 62. The outer end of the screwelement 51 projects beyond the end of the case 50, and this projectingportion is enlarged in diameter to provide a knob 70. Closely adjacentthe knob 70, the tubular element 51 is provided pin 72 projectinginwardly from the case 50, so as to hold the members 59, 51 againstendwise separation, While permitting free rotatio'n relative to oneanother.

Thetubular element 51 has a helical groove or slot 73 formed therein,which extends `for the greater part of the length of the element. A pin74 projecting upwardly from the top vof the carrier 6l, passes throughthe helical slot 73 of the tubular element 5l, and its end is slidablyreceived within the longitudinally extending groove 60 in thecylindrical case 50.

The slider, or carrier 61 may have the form shown in Figure 7, whereinits cross sectional shape is the segment of a circle, with thecylindrical top surface thereof fitted to the inside surface ofthe-tubular element 51. Attached to the at bottom surface of the carrieris a U- shaped spring contact 75, one arm 76 of which wipes on theresistance element 65, while the other arm 77 wipes on the conductorstrip 66.

From the foregoing description, it will be understood by thoseskilled inthe art that rotation of the tubular screw element 51 relative to thecylindrical case 56 causes the carrier 61 to be shifted lengthwise ofthe resistance element 65 and conductor strip 66, owing to cammingeffect of the helical slot 73 on the pin 74. The carrier `61 is, ofcoulse, kept from turningwith vthe screw element 50 bytheslidingengagement of the Vpin 74 in the groove 60.

While I have shown and described in considerable-detail twoselectedembodiments .of the invention, it will be understood by thoseskilledin the art that these are merely illustrative of the principlesof the invention, and various changes maybe made in the shape andarrangement or disposition of the several parts without departing fromthe broad scope of the invention, as dened in the following claims.

I claim:

l. A variable resistor comprising: a tubular case; a female thread insaid case; a slider having a male thread engaging saidfemale thread; anon-round opening in said slider; a mounting member insaid case andhaving a matching non-round cross section; said slider being slidablymounted on said mounting; a resistance element secured on said mountingon one side thereof; contact means carried by said slider having acontact arm engaging said resistance element and means carriedrby saidcase and said mounting preventing relative longitudinal movement thereof.but permittingrrelative rotation `thereof whereby said spring contactarm is carried to travel over `said element.

2. .A variable resistor, comprising a body made up of tworelativelyrotatable parts, one of said parts being hollow and having ahelicalfthread formed thereon, and the other-part having a projectingkportionextending -into the hollow lcenter ofsaidone part, parallel tothe longitudinal axis thereof, a resistance element mounted on saidprojecting portion, and a slider movable along the lengthlof saidprojecting -portion and having a `contact wiping on .said resistanceelement, said sliderbeing engaged-by saidhelical thread .andbeingmovablethereby whensaid body .parts are rotated with respect to'one another.

3. A var iable resistor comprising a body made up of a stationarymember.and Va `rotatable sleeve member vhaving aninternal thread formedthereon; a projection on said stationary member extendingparallel to theaxis of'said rotatablesleevememben said projection having a nonroundcross section, a resistance element mounted'on said projection, asliderslidably mounted on said projectionand restrained thereby againstrotation, said slider havingan external thread coacting with saidinternal thread onsaid sleevememben'whereby the slider is movedlengthwise of -said projection when said sleeve member is rotated,` anda contact on said slider engaging said resistance element. Y

4.1 Avariable resistor comprising a generally cylindrical member havingahelixformed thereon, aresistance element mounted within saidcylindrical member generally parallel to the axis thereof, a carriermounted within said cylindrical member and having a contact wiping onsaid resistance element, means on said carrier engaging said helixwhereby rotation of said cylindrical member with respect to saidresistance element causes said carrier t0 be moved lengthwise along saidelement, said carrier being restrained against rotation with saidcylindrical member, and electrical return means from said contact to anexternal terminal means.

5. A variable resistor comprising a body made up of two relativelyrotatable members, one of said members having a helix formed thereon, aresistance element mounted on the other of said members generallyparallel to the longitudinal axis thereof, a carrier movable lengthwiseof said resistance element and having a contact wiping thereon, meansrestraining said carrier against rotation while permitting free movementthereof along the length-of said resistance element, means on saidcarrier engaging saidhelix'whereby rotation of said one member withrespect to Vsaid other member causes said carrier tomove along saidelement,and electrical return means from said contact to an externalterminal means.

6. A variable resistor comprising a body made up of two relativelyrotatable members, one of said members havingga helix formed thereon, aresistance element mounted onthe other of said members generallyparallel to the longitudinal 'axis thereof, a carrier movable lengthwiseof said resistance element and having a contact wiping thereon, saidcarrier having apart slidably engaging said other member-so as torestrain it from turning while permitting free movement thereof alongthe length of Said resistance element, said carrier being operativelyengaged by said helix whereby rotation of said one -member with respectto said other member causes said carrier to move along said element, andelectrical return means from said contact to an external terminal means.

7. A` variable resistor comprising, in combination, a body member havinga resistance element mounted thereon, a slidable carrier having acontact wiping on said resistance element, a tubular member rotatablymounted on said body member and enclosing said carrier and saidresistance element, said carrier being restrained against rotationrelative to said body member vwhile permitted free sliding movement withrespect thereto, and means operatively connecting saidcarrier with saidrotatable tubular member to shift the carrier lengthwise along saidresistance element as saidtubular member is rotated with respect to saidbody member.

V8. A variable resistor as recited in claim 5 lwherein said one membercomprises a hollow cylinder,lthe helix formed onrsaid one of saidmembers comprises a helical slot through the walls of said hollowcylinder, said means 0n said carrierengaging-said helix comprises a pinextending through said helical slot, said other of saidrelativelyrotatable memberscomprises ahollow cylinder having an endwall, a projecting portion extendingfrom said end wallinto ythe cavityofrsaid cylinder-and being spaced sufficiently from-the sideszthereofto-enable said one member to be linserted therein, said resistance.winding being mounted yonsaid projection, said means restraining saidcarrier against rotation while permitting free movement thereoflalong'the length of said .resistance element comprises a .longitudinalgroove in .said other of said relatively rotatable members into whichsaid pin extends, and said electrical return means from saidcontact-toan external terminal means includes anelongated conductor mountedparallel to said resistance winding on said projection, and-a secondcontact carried by said carrier and wipingron,saidconducton said secondcontact being `electrically connected .to said Contact wiping on saidresistance.

9. A variable resistor as recited in claim 6 wherein said one of lsaidmembers having a helix formed thereon comprises ahollow cylinder withsaid helix being in the form Qf'a slot, said other of said tworelatively rotatable members also comprises a hollow cylinder withinwhich said tirst hollow member lits, said other of said two relativelyrotatable members including means for supporting said resistance elementwithin said one of said members, said other of said two relativelyrotatable members including a slot extending parallel to itslongitudinal axis, and said part of said carrier slidably engaging saidother member so as to restrain itvfrom turning While permitting freemovement thereof along the length of said resistance element comprises apost on said carrier extending through said helical slot into saidgroove.

l0. A variable resistor as recited in claim'6 wherein said electricalreturn means includes an elongated conduc- 6 tor means for mounting saidelongated conductor on the other of said members parallel to saidresistance element, a second contact carrier by said carrier for wipingon said conductor, said second contact being electrically connected tosaid contact wiping on said resistance.

References Cited in the file of this patent UNITED STATES PATENTS2,523,896 Bartolomei Sept. 26, 1950 2,704,860 Graybeal et al May 22,1955 2,714,147 Reid -1. July 26, 1955 2,769,073 Gintovt 4.---., Oct. 30,1956

